Merge tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes, perhaps most notably:

      - Throttling callback invocation based on the number of callbacks
        that are now ready to invoke instead of on the total number of
        callbacks

      - Several patches that suppress false-positive boot-time
        diagnostics, for example, due to lockdep not yet being
        initialized

      - Make expedited RCU CPU stall warnings dump stacks of any tasks
        that are blocking the stalled grace period. (Normal RCU CPU
        stall warnings have done this for many years)

      - Lazy-callback fixes to avoid delays during boot, suspend, and
        resume. (Note that lazy callbacks must be explicitly enabled, so
        this should not (yet) affect production use cases)

 - Make kfree_rcu() and friends take advantage of polled grace periods,
   thus reducing memory footprint by almost two orders of magnitude,
   admittedly on a microbenchmark

   This also begins the transition from kfree_rcu(p) to
   kfree_rcu_mightsleep(p). This transition was motivated by bugs where
   kfree_rcu(p), which can block, was typed instead of the intended
   kfree_rcu(p, rh)

 - SRCU updates, perhaps most notably fixing a bug that causes SRCU to
   fail when booted on a system with a non-zero boot CPU. This
   surprising situation actually happens for kdump kernels on the
   powerpc architecture

   This also adds an srcu_down_read() and srcu_up_read(), which act like
   srcu_read_lock() and srcu_read_unlock(), but allow an SRCU read-side
   critical section to be handed off from one task to another

 - Clean up the now-useless SRCU Kconfig option

   There are a few more commits that are not yet acked or pulled into
   maintainer trees, and these will be in a pull request for a later
   merge window

 - RCU-tasks updates, perhaps most notably these fixes:

      - A strange interaction between PID-namespace unshare and the
        RCU-tasks grace period that results in a low-probability but
        very real hang

      - A race between an RCU tasks rude grace period on a single-CPU
        system and CPU-hotplug addition of the second CPU that can
        result in a too-short grace period

      - A race between shrinking RCU tasks down to a single callback
        list and queuing a new callback to some other CPU, but where
        that queuing is delayed for more than an RCU grace period. This
        can result in that callback being stranded on the non-boot CPU

 - Torture-test updates and fixes

 - Torture-test scripting updates and fixes

 - Provide additional RCU CPU stall-warning information in kernels built
   with CONFIG_RCU_CPU_STALL_CPUTIME=y, and restore the full five-minute
   timeout limit for expedited RCU CPU stall warnings

* tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu/kvfree: Add kvfree_rcu_mightsleep() and kfree_rcu_mightsleep()
  kernel/notifier: Remove CONFIG_SRCU
  init: Remove "select SRCU"
  fs/quota: Remove "select SRCU"
  fs/notify: Remove "select SRCU"
  fs/btrfs: Remove "select SRCU"
  fs: Remove CONFIG_SRCU
  drivers/pci/controller: Remove "select SRCU"
  drivers/net: Remove "select SRCU"
  drivers/md: Remove "select SRCU"
  drivers/hwtracing/stm: Remove "select SRCU"
  drivers/dax: Remove "select SRCU"
  drivers/base: Remove CONFIG_SRCU
  rcu: Disable laziness if lazy-tracking says so
  rcu: Track laziness during boot and suspend
  rcu: Remove redundant call to rcu_boost_kthread_setaffinity()
  rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts
  rcu: Align the output of RCU CPU stall warning messages
  rcu: Add RCU stall diagnosis information
  sched: Add helper nr_context_switches_cpu()
  ...

Documentation/RCU/NMI-RCU.rst

@@ -8,7 +8,7 @@ Although RCU is usually used to protect read-mostly data structures,
 it is possible to use RCU to provide dynamic non-maskable interrupt
 handlers, as well as dynamic irq handlers.  This document describes
 how to do this, drawing loosely from Zwane Mwaikambo's NMI-timer
-work in "arch/x86/kernel/traps.c".
+work in an old version of "arch/x86/kernel/traps.c".
 
 The relevant pieces of code are listed below, each followed by a
 brief explanation::
@@ -116,7 +116,7 @@ Answer to Quick Quiz:
 
 	This same sad story can happen on other CPUs when using
 	a compiler with aggressive pointer-value speculation
-	optimizations.
+	optimizations.  (But please don't!)
 
 	More important, the rcu_dereference_sched() makes it
 	clear to someone reading the code that the pointer is

Documentation/RCU/UP.rst

@@ -38,7 +38,7 @@ by having call_rcu() directly invoke its arguments only if it was called
 from process context.  However, this can fail in a similar manner.
 
 Suppose that an RCU-based algorithm again scans a linked list containing
-elements A, B, and C in process contexts, but that it invokes a function
+elements A, B, and C in process context, but that it invokes a function
 on each element as it is scanned.  Suppose further that this function
 deletes element B from the list, then passes it to call_rcu() for deferred
 freeing.  This may be a bit unconventional, but it is perfectly legal
@@ -59,7 +59,8 @@ Example 3: Death by Deadlock
 Suppose that call_rcu() is invoked while holding a lock, and that the
 callback function must acquire this same lock.  In this case, if
 call_rcu() were to directly invoke the callback, the result would
-be self-deadlock.
+be self-deadlock *even if* this invocation occurred from a later
+call_rcu() invocation a full grace period later.
 
 In some cases, it would possible to restructure to code so that
 the call_rcu() is delayed until after the lock is released.  However,
@@ -85,6 +86,14 @@ Quick Quiz #2:
 
 :ref:`Answers to Quick Quiz <answer_quick_quiz_up>`
 
+It is important to note that userspace RCU implementations *do*
+permit call_rcu() to directly invoke callbacks, but only if a full
+grace period has elapsed since those callbacks were queued.  This is
+the case because some userspace environments are extremely constrained.
+Nevertheless, people writing userspace RCU implementations are strongly
+encouraged to avoid invoking callbacks from call_rcu(), thus obtaining
+the deadlock-avoidance benefits called out above.
+
 Summary
 -------
 

Documentation/RCU/lockdep.rst

@@ -69,9 +69,8 @@ checking of rcu_dereference() primitives:
 		value of the pointer itself, for example, against NULL.
 
 The rcu_dereference_check() check expression can be any boolean
-expression, but would normally include a lockdep expression.  However,
-any boolean expression can be used.  For a moderately ornate example,
-consider the following::
+expression, but would normally include a lockdep expression.  For a
+moderately ornate example, consider the following::
 
 	file = rcu_dereference_check(fdt->fd[fd],
 				     lockdep_is_held(&files->file_lock) ||
@@ -97,10 +96,10 @@ code, it could instead be written as follows::
 					 atomic_read(&files->count) == 1);
 
 This would verify cases #2 and #3 above, and furthermore lockdep would
-complain if this was used in an RCU read-side critical section unless one
-of these two cases held.  Because rcu_dereference_protected() omits all
-barriers and compiler constraints, it generates better code than do the
-other flavors of rcu_dereference().  On the other hand, it is illegal
+complain even if this was used in an RCU read-side critical section unless
+one of these two cases held.  Because rcu_dereference_protected() omits
+all barriers and compiler constraints, it generates better code than do
+the other flavors of rcu_dereference().  On the other hand, it is illegal
 to use rcu_dereference_protected() if either the RCU-protected pointer
 or the RCU-protected data that it points to can change concurrently.
 

Documentation/RCU/rcu.rst

@@ -77,15 +77,17 @@ Frequently Asked Questions
   search for the string "Patent" in Documentation/RCU/RTFP.txt to find them.
   Of these, one was allowed to lapse by the assignee, and the
   others have been contributed to the Linux kernel under GPL.
+  Many (but not all) have long since expired.
   There are now also LGPL implementations of user-level RCU
   available (https://liburcu.org/).
 
 - I hear that RCU needs work in order to support realtime kernels?
 
-  Realtime-friendly RCU can be enabled via the CONFIG_PREEMPT_RCU
+  Realtime-friendly RCU are enabled via the CONFIG_PREEMPTION
   kernel configuration parameter.
 
 - Where can I find more information on RCU?
 
   See the Documentation/RCU/RTFP.txt file.
-  Or point your browser at (http://www.rdrop.com/users/paulmck/RCU/).
+  Or point your browser at (https://docs.google.com/document/d/1X0lThx8OK0ZgLMqVoXiR4ZrGURHrXK6NyLRbeXe3Xac/edit)
+  or (https://docs.google.com/document/d/1GCdQC8SDbb54W1shjEXqGZ0Rq8a6kIeYutdSIajfpLA/edit?usp=sharing).

Documentation/RCU/rcu_dereference.rst

@@ -19,8 +19,9 @@ Follow these rules to keep your RCU code working properly:
 	can reload the value, and won't your code have fun with two
 	different values for a single pointer!  Without rcu_dereference(),
 	DEC Alpha can load a pointer, dereference that pointer, and
-	return data preceding initialization that preceded the store of
-	the pointer.
+	return data preceding initialization that preceded the store
+	of the pointer.  (As noted later, in recent kernels READ_ONCE()
+	also prevents DEC Alpha from playing these tricks.)
 
 	In addition, the volatile cast in rcu_dereference() prevents the
 	compiler from deducing the resulting pointer value.  Please see
@@ -34,7 +35,7 @@ Follow these rules to keep your RCU code working properly:
 	takes on the role of the lockless_dereference() primitive that
 	was removed in v4.15.
 
--	You are only permitted to use rcu_dereference on pointer values.
+-	You are only permitted to use rcu_dereference() on pointer values.
 	The compiler simply knows too much about integral values to
 	trust it to carry dependencies through integer operations.
 	There are a very few exceptions, namely that you can temporarily
@@ -240,6 +241,7 @@ precautions.  To see this, consider the following code fragment::
 		struct foo *q;
 		int r1, r2;
 
+		rcu_read_lock();
 		p = rcu_dereference(gp2);
 		if (p == NULL)
 			return;
@@ -248,7 +250,10 @@ precautions.  To see this, consider the following code fragment::
 		if (p == q) {
 			/* The compiler decides that q->c is same as p->c. */
 			r2 = p->c; /* Could get 44 on weakly order system. */
+		} else {
+			r2 = p->c - r1; /* Unconditional access to p->c. */
 		}
+		rcu_read_unlock();
 		do_something_with(r1, r2);
 	}
 
@@ -297,6 +302,7 @@ Then one approach is to use locking, for example, as follows::
 		struct foo *q;
 		int r1, r2;
 
+		rcu_read_lock();
 		p = rcu_dereference(gp2);
 		if (p == NULL)
 			return;
@@ -306,7 +312,12 @@ Then one approach is to use locking, for example, as follows::
 		if (p == q) {
 			/* The compiler decides that q->c is same as p->c. */
 			r2 = p->c; /* Locking guarantees r2 == 144. */
+		} else {
+			spin_lock(&q->lock);
+			r2 = q->c - r1;
+			spin_unlock(&q->lock);
 		}
+		rcu_read_unlock();
 		spin_unlock(&p->lock);
 		do_something_with(r1, r2);
 	}
@@ -364,7 +375,7 @@ the exact value of "p" even in the not-equals case.  This allows the
 compiler to make the return values independent of the load from "gp",
 in turn destroying the ordering between this load and the loads of the
 return values.  This can result in "p->b" returning pre-initialization
-garbage values.
+garbage values on weakly ordered systems.
 
 In short, rcu_dereference() is *not* optional when you are going to
 dereference the resulting pointer.
@@ -430,7 +441,7 @@ member of the rcu_dereference() to use in various situations:
 SPARSE CHECKING OF RCU-PROTECTED POINTERS
 -----------------------------------------
 
-The sparse static-analysis tool checks for direct access to RCU-protected
+The sparse static-analysis tool checks for non-RCU access to RCU-protected
 pointers, which can result in "interesting" bugs due to compiler
 optimizations involving invented loads and perhaps also load tearing.
 For example, suppose someone mistakenly does something like this::

Documentation/RCU/rculist_nulls.rst

@@ -14,19 +14,19 @@ Using 'nulls'
 =============
 
 Using special makers (called 'nulls') is a convenient way
-to solve following problem :
+to solve following problem.
 
-A typical RCU linked list managing objects which are
-allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can
-use following algos :
+Without 'nulls', a typical RCU linked list managing objects which are
+allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can use the following
+algorithms:
 
-1) Lookup algo
---------------
+1) Lookup algorithm
+-------------------
 
 ::
 
-  rcu_read_lock()
   begin:
+  rcu_read_lock()
   obj = lockless_lookup(key);
   if (obj) {
     if (!try_get_ref(obj)) // might fail for free objects
@@ -38,6 +38,7 @@ use following algos :
     */
     if (obj->key != key) { // not the object we expected
       put_ref(obj);
+      rcu_read_unlock();
       goto begin;
     }
   }
@@ -52,9 +53,9 @@ but a version with an additional memory barrier (smp_rmb())
   {
     struct hlist_node *node, *next;
     for (pos = rcu_dereference((head)->first);
-        pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) &&
-        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
-        pos = rcu_dereference(next))
+         pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) &&
+         ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
+         pos = rcu_dereference(next))
       if (obj->key == key)
         return obj;
     return NULL;
@@ -64,9 +65,9 @@ And note the traditional hlist_for_each_entry_rcu() misses this smp_rmb()::
 
   struct hlist_node *node;
   for (pos = rcu_dereference((head)->first);
-        pos && ({ prefetch(pos->next); 1; }) &&
-        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
-        pos = rcu_dereference(pos->next))
+       pos && ({ prefetch(pos->next); 1; }) &&
+       ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
+       pos = rcu_dereference(pos->next))
    if (obj->key == key)
      return obj;
   return NULL;
@@ -82,36 +83,32 @@ Quoting Corey Minyard::
   solved by pre-fetching the "next" field (with proper barriers) before
   checking the key."
 
-2) Insert algo
---------------
+2) Insertion algorithm
+----------------------
 
 We need to make sure a reader cannot read the new 'obj->obj_next' value
-and previous value of 'obj->key'. Or else, an item could be deleted
+and previous value of 'obj->key'. Otherwise, an item could be deleted
 from a chain, and inserted into another chain. If new chain was empty
-before the move, 'next' pointer is NULL, and lockless reader can
-not detect it missed following items in original chain.
+before the move, 'next' pointer is NULL, and lockless reader can not
+detect the fact that it missed following items in original chain.
 
 ::
 
   /*
-  * Please note that new inserts are done at the head of list,
-  * not in the middle or end.
-  */
+   * Please note that new inserts are done at the head of list,
+   * not in the middle or end.
+   */
   obj = kmem_cache_alloc(...);
   lock_chain(); // typically a spin_lock()
   obj->key = key;
-  /*
-  * we need to make sure obj->key is updated before obj->next
-  * or obj->refcnt
-  */
-  smp_wmb();
-  atomic_set(&obj->refcnt, 1);
+  atomic_set_release(&obj->refcnt, 1); // key before refcnt
   hlist_add_head_rcu(&obj->obj_node, list);
   unlock_chain(); // typically a spin_unlock()
 
 
-3) Remove algo
---------------
+3) Removal algorithm
+--------------------
+
 Nothing special here, we can use a standard RCU hlist deletion.
 But thanks to SLAB_TYPESAFE_BY_RCU, beware a deleted object can be reused
 very very fast (before the end of RCU grace period)
@@ -133,7 +130,7 @@ Avoiding extra smp_rmb()
 ========================
 
 With hlist_nulls we can avoid extra smp_rmb() in lockless_lookup()
-and extra smp_wmb() in insert function.
+and extra _release() in insert function.
 
 For example, if we choose to store the slot number as the 'nulls'
 end-of-list marker for each slot of the hash table, we can detect
@@ -142,59 +139,61 @@ to another chain) checking the final 'nulls' value if
 the lookup met the end of chain. If final 'nulls' value
 is not the slot number, then we must restart the lookup at
 the beginning. If the object was moved to the same chain,
-then the reader doesn't care : It might eventually
+then the reader doesn't care: It might occasionally
 scan the list again without harm.
 
 
-1) lookup algo
---------------
+1) lookup algorithm
+-------------------
 
 ::
 
   head = &table[slot];
-  rcu_read_lock();
   begin:
+  rcu_read_lock();
   hlist_nulls_for_each_entry_rcu(obj, node, head, member) {
     if (obj->key == key) {
-      if (!try_get_ref(obj)) // might fail for free objects
+      if (!try_get_ref(obj)) { // might fail for free objects
+	rcu_read_unlock();
         goto begin;
+      }
       if (obj->key != key) { // not the object we expected
         put_ref(obj);
+	rcu_read_unlock();
         goto begin;
       }
-    goto out;
+      goto out;
+    }
+  }
+
+  // If the nulls value we got at the end of this lookup is
+  // not the expected one, we must restart lookup.
+  // We probably met an item that was moved to another chain.
+  if (get_nulls_value(node) != slot) {
+    put_ref(obj);
+    rcu_read_unlock();
+    goto begin;
   }
-  /*
-  * if the nulls value we got at the end of this lookup is
-  * not the expected one, we must restart lookup.
-  * We probably met an item that was moved to another chain.
-  */
-  if (get_nulls_value(node) != slot)
-  goto begin;
   obj = NULL;
 
   out:
   rcu_read_unlock();
 
-2) Insert function
-------------------
+2) Insert algorithm
+-------------------
 
 ::
 
   /*
-  * Please note that new inserts are done at the head of list,
-  * not in the middle or end.
-  */
+   * Please note that new inserts are done at the head of list,
+   * not in the middle or end.
+   */
   obj = kmem_cache_alloc(cachep);
   lock_chain(); // typically a spin_lock()
   obj->key = key;
+  atomic_set_release(&obj->refcnt, 1); // key before refcnt
   /*
-  * changes to obj->key must be visible before refcnt one
-  */
-  smp_wmb();
-  atomic_set(&obj->refcnt, 1);
-  /*
-  * insert obj in RCU way (readers might be traversing chain)
-  */
+   * insert obj in RCU way (readers might be traversing chain)
+   */
   hlist_nulls_add_head_rcu(&obj->obj_node, list);
   unlock_chain(); // typically a spin_unlock()

Documentation/RCU/stallwarn.rst

@@ -25,10 +25,10 @@ warnings:
 
 -	A CPU looping with bottom halves disabled.
 
--	For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the kernel
-	without invoking schedule().  If the looping in the kernel is
-	really expected and desirable behavior, you might need to add
-	some calls to cond_resched().
+-	For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the
+	kernel without potentially invoking schedule().  If the looping
+	in the kernel is really expected and desirable behavior, you
+	might need to add some calls to cond_resched().
 
 -	Booting Linux using a console connection that is too slow to
 	keep up with the boot-time console-message rate.  For example,
@@ -108,16 +108,17 @@ warnings:
 
 -	A bug in the RCU implementation.
 
--	A hardware failure.  This is quite unlikely, but has occurred
-	at least once in real life.  A CPU failed in a running system,
-	becoming unresponsive, but not causing an immediate crash.
-	This resulted in a series of RCU CPU stall warnings, eventually
-	leading the realization that the CPU had failed.
+-	A hardware failure.  This is quite unlikely, but is not at all
+	uncommon in large datacenter.  In one memorable case some decades
+	back, a CPU failed in a running system, becoming unresponsive,
+	but not causing an immediate crash.  This resulted in a series
+	of RCU CPU stall warnings, eventually leading the realization
+	that the CPU had failed.
 
-The RCU, RCU-sched, and RCU-tasks implementations have CPU stall warning.
-Note that SRCU does *not* have CPU stall warnings.  Please note that
-RCU only detects CPU stalls when there is a grace period in progress.
-No grace period, no CPU stall warnings.
+The RCU, RCU-sched, RCU-tasks, and RCU-tasks-trace implementations have
+CPU stall warning.  Note that SRCU does *not* have CPU stall warnings.
+Please note that RCU only detects CPU stalls when there is a grace period
+in progress.  No grace period, no CPU stall warnings.
 
 To diagnose the cause of the stall, inspect the stack traces.
 The offending function will usually be near the top of the stack.
@@ -205,16 +206,21 @@ RCU_STALL_RAT_DELAY
 rcupdate.rcu_task_stall_timeout
 -------------------------------
 
-	This boot/sysfs parameter controls the RCU-tasks stall warning
-	interval.  A value of zero or less suppresses RCU-tasks stall
-	warnings.  A positive value sets the stall-warning interval
-	in seconds.  An RCU-tasks stall warning starts with the line:
+	This boot/sysfs parameter controls the RCU-tasks and
+	RCU-tasks-trace stall warning intervals.  A value of zero or less
+	suppresses RCU-tasks stall warnings.  A positive value sets the
+	stall-warning interval in seconds.  An RCU-tasks stall warning
+	starts with the line:
 
 		INFO: rcu_tasks detected stalls on tasks:
 
 	And continues with the output of sched_show_task() for each
 	task stalling the current RCU-tasks grace period.
 
+	An RCU-tasks-trace stall warning starts (and continues) similarly:
+
+		INFO: rcu_tasks_trace detected stalls on tasks
+
 
 Interpreting RCU's CPU Stall-Detector "Splats"
 ==============================================
@@ -248,7 +254,8 @@ dynticks counter, which will have an even-numbered value if the CPU
 is in dyntick-idle mode and an odd-numbered value otherwise.  The hex
 number between the two "/"s is the value of the nesting, which will be
 a small non-negative number if in the idle loop (as shown above) and a
-very large positive number otherwise.
+very large positive number otherwise.  The number following the final
+"/" is the NMI nesting, which will be a small non-negative number.
 
 The "softirq=" portion of the message tracks the number of RCU softirq
 handlers that the stalled CPU has executed.  The number before the "/"
@@ -383,3 +390,95 @@ for example, "P3421".
 
 It is entirely possible to see stall warnings from normal and from
 expedited grace periods at about the same time during the same run.
+
+RCU_CPU_STALL_CPUTIME
+=====================
+
+In kernels built with CONFIG_RCU_CPU_STALL_CPUTIME=y or booted with
+rcupdate.rcu_cpu_stall_cputime=1, the following additional information
+is supplied with each RCU CPU stall warning::
+
+  rcu:          hardirqs   softirqs   csw/system
+  rcu:  number:      624         45            0
+  rcu: cputime:       69          1         2425   ==> 2500(ms)
+
+These statistics are collected during the sampling period. The values
+in row "number:" are the number of hard interrupts, number of soft
+interrupts, and number of context switches on the stalled CPU. The
+first three values in row "cputime:" indicate the CPU time in
+milliseconds consumed by hard interrupts, soft interrupts, and tasks
+on the stalled CPU.  The last number is the measurement interval, again
+in milliseconds.  Because user-mode tasks normally do not cause RCU CPU
+stalls, these tasks are typically kernel tasks, which is why only the
+system CPU time are considered.
+
+The sampling period is shown as follows::
+
+  |<------------first timeout---------->|<-----second timeout----->|
+  |<--half timeout-->|<--half timeout-->|                          |
+  |                  |<--first period-->|                          |
+  |                  |<-----------second sampling period---------->|
+  |                  |                  |                          |
+             snapshot time point    1st-stall                  2nd-stall
+
+The following describes four typical scenarios:
+
+1. A CPU looping with interrupts disabled.
+
+   ::
+
+     rcu:          hardirqs   softirqs   csw/system
+     rcu:  number:        0          0            0
+     rcu: cputime:        0          0            0   ==> 2500(ms)
+
+   Because interrupts have been disabled throughout the measurement
+   interval, there are no interrupts and no context switches.
+   Furthermore, because CPU time consumption was measured using interrupt
+   handlers, the system CPU consumption is misleadingly measured as zero.
+   This scenario will normally also have "(0 ticks this GP)" printed on
+   this CPU's summary line.
+
+2. A CPU looping with bottom halves disabled.
+
+   This is similar to the previous example, but with non-zero number of
+   and CPU time consumed by hard interrupts, along with non-zero CPU
+   time consumed by in-kernel execution::
+
+     rcu:          hardirqs   softirqs   csw/system
+     rcu:  number:      624          0            0
+     rcu: cputime:       49          0         2446   ==> 2500(ms)
+
+   The fact that there are zero softirqs gives a hint that these were
+   disabled, perhaps via local_bh_disable().  It is of course possible
+   that there were no softirqs, perhaps because all events that would
+   result in softirq execution are confined to other CPUs.  In this case,
+   the diagnosis should continue as shown in the next example.
+
+3. A CPU looping with preemption disabled.
+
+   Here, only the number of context switches is zero::
+
+     rcu:          hardirqs   softirqs   csw/system
+     rcu:  number:      624         45            0
+     rcu: cputime:       69          1         2425   ==> 2500(ms)
+
+   This situation hints that the stalled CPU was looping with preemption
+   disabled.
+
+4. No looping, but massive hard and soft interrupts.
+
+   ::
+
+     rcu:          hardirqs   softirqs   csw/system
+     rcu:  number:       xx         xx            0
+     rcu: cputime:       xx         xx            0   ==> 2500(ms)
+
+   Here, the number and CPU time of hard interrupts are all non-zero,
+   but the number of context switches and the in-kernel CPU time consumed
+   are zero. The number and cputime of soft interrupts will usually be
+   non-zero, but could be zero, for example, if the CPU was spinning
+   within a single hard interrupt handler.
+
+   If this type of RCU CPU stall warning can be reproduced, you can
+   narrow it down by looking at /proc/interrupts or by writing code to
+   trace each interrupt, for example, by referring to show_interrupts().

Documentation/RCU/torture.rst

@@ -206,7 +206,11 @@ values for memory may require disabling the callback-flooding tests
 using the --bootargs parameter discussed below.
 
 Sometimes additional debugging is useful, and in such cases the --kconfig
-parameter to kvm.sh may be used, for example, ``--kconfig 'CONFIG_KASAN=y'``.
+parameter to kvm.sh may be used, for example, ``--kconfig 'CONFIG_RCU_EQS_DEBUG=y'``.
+In addition, there are the --gdb, --kasan, and --kcsan parameters.
+Note that --gdb limits you to one scenario per kvm.sh run and requires
+that you have another window open from which to run ``gdb`` as instructed
+by the script.
 
 Kernel boot arguments can also be supplied, for example, to control
 rcutorture's module parameters.  For example, to test a change to RCU's
@@ -219,10 +223,17 @@ require disabling rcutorture's callback-flooding tests::
 		--bootargs 'rcutorture.fwd_progress=0'
 
 Sometimes all that is needed is a full set of kernel builds.  This is
-what the --buildonly argument does.
+what the --buildonly parameter does.
 
-Finally, the --trust-make argument allows each kernel build to reuse what
-it can from the previous kernel build.
+The --duration parameter can override the default run time of 30 minutes.
+For example, ``--duration 2d`` would run for two days, ``--duration 3h``
+would run for three hours, ``--duration 5m`` would run for five minutes,
+and ``--duration 45s`` would run for 45 seconds.  This last can be useful
+for tracking down rare boot-time failures.
+
+Finally, the --trust-make parameter allows each kernel build to reuse what
+it can from the previous kernel build.  Please note that without the
+--trust-make parameter, your tags files may be demolished.
 
 There are additional more arcane arguments that are documented in the
 source code of the kvm.sh script.
@@ -291,3 +302,73 @@ the following summary at the end of the run on a 12-CPU system::
     TREE07 ------- 167347 GPs (30.9902/s) [rcu: g1079021 f0x0 ] n_max_cbs: 478732
     CPU count limited from 16 to 12
     TREE09 ------- 752238 GPs (139.303/s) [rcu: g13075057 f0x0 ] n_max_cbs: 99011
+
+
+Repeated Runs
+=============
+
+Suppose that you are chasing down a rare boot-time failure.  Although you
+could use kvm.sh, doing so will rebuild the kernel on each run.  If you
+need (say) 1,000 runs to have confidence that you have fixed the bug,
+these pointless rebuilds can become extremely annoying.
+
+This is why kvm-again.sh exists.
+
+Suppose that a previous kvm.sh run left its output in this directory::
+
+	tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28
+
+Then this run can be re-run without rebuilding as follow:
+
+	kvm-again.sh tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28
+
+A few of the original run's kvm.sh parameters may be overridden, perhaps
+most notably --duration and --bootargs.  For example::
+
+	kvm-again.sh tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28 \
+		--duration 45s
+
+would re-run the previous test, but for only 45 seconds, thus facilitating
+tracking down the aforementioned rare boot-time failure.
+
+
+Distributed Runs
+================
+
+Although kvm.sh is quite useful, its testing is confined to a single
+system.  It is not all that hard to use your favorite framework to cause
+(say) 5 instances of kvm.sh to run on your 5 systems, but this will very
+likely unnecessarily rebuild kernels.  In addition, manually distributing
+the desired rcutorture scenarios across the available systems can be
+painstaking and error-prone.
+
+And this is why the kvm-remote.sh script exists.
+
+If you the following command works::
+
+	ssh system0 date
+
+and if it also works for system1, system2, system3, system4, and system5,
+and all of these systems have 64 CPUs, you can type::
+
+	kvm-remote.sh "system0 system1 system2 system3 system4 system5" \
+		--cpus 64 --duration 8h --configs "5*CFLIST"
+
+This will build each default scenario's kernel on the local system, then
+spread each of five instances of each scenario over the systems listed,
+running each scenario for eight hours.  At the end of the runs, the
+results will be gathered, recorded, and printed.  Most of the parameters
+that kvm.sh will accept can be passed to kvm-remote.sh, but the list of
+systems must come first.
+
+The kvm.sh ``--dryrun scenarios`` argument is useful for working out
+how many scenarios may be run in one batch across a group of systems.
+
+You can also re-run a previous remote run in a manner similar to kvm.sh:
+
+	kvm-remote.sh "system0 system1 system2 system3 system4 system5" \
+		tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28-remote \
+		--duration 24h
+
+In this case, most of the kvm-again.sh parmeters may be supplied following
+the pathname of the old run-results directory.

Documentation/admin-guide/kernel-parameters.txt

@@ -5113,6 +5113,17 @@
 			rcupdate.rcu_cpu_stall_timeout to be used (after
 			conversion from seconds to milliseconds).
 
+	rcupdate.rcu_cpu_stall_cputime= [KNL]
+			Provide statistics on the cputime and count of
+			interrupts and tasks during the sampling period. For
+			multiple continuous RCU stalls, all sampling periods
+			begin at half of the first RCU stall timeout.
+
+	rcupdate.rcu_exp_stall_task_details= [KNL]
+			Print stack dumps of any tasks blocking the
+			current expedited RCU grace period during an
+			expedited RCU CPU stall warning.
+
 	rcupdate.rcu_expedited= [KNL]
 			Use expedited grace-period primitives, for
 			example, synchronize_rcu_expedited() instead

drivers/base/core.c

@@ -181,7 +181,6 @@ void fw_devlink_purge_absent_suppliers(struct fwnode_handle *fwnode)
 }
 EXPORT_SYMBOL_GPL(fw_devlink_purge_absent_suppliers);
 
-#ifdef CONFIG_SRCU
 static DEFINE_MUTEX(device_links_lock);
 DEFINE_STATIC_SRCU(device_links_srcu);
 
@@ -220,47 +219,6 @@ static void device_link_remove_from_lists(struct device_link *link)
 	list_del_rcu(&link->s_node);
 	list_del_rcu(&link->c_node);
 }
-#else /* !CONFIG_SRCU */
-static DECLARE_RWSEM(device_links_lock);
-
-static inline void device_links_write_lock(void)
-{
-	down_write(&device_links_lock);
-}
-
-static inline void device_links_write_unlock(void)
-{
-	up_write(&device_links_lock);
-}
-
-int device_links_read_lock(void)
-{
-	down_read(&device_links_lock);
-	return 0;
-}
-
-void device_links_read_unlock(int not_used)
-{
-	up_read(&device_links_lock);
-}
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-int device_links_read_lock_held(void)
-{
-	return lockdep_is_held(&device_links_lock);
-}
-#endif
-
-static inline void device_link_synchronize_removal(void)
-{
-}
-
-static void device_link_remove_from_lists(struct device_link *link)
-{
-	list_del(&link->s_node);
-	list_del(&link->c_node);
-}
-#endif /* !CONFIG_SRCU */
 
 static bool device_is_ancestor(struct device *dev, struct device *target)
 {

drivers/dax/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 menuconfig DAX
 	tristate "DAX: direct access to differentiated memory"
-	select SRCU
 	default m if NVDIMM_DAX
 
 if DAX

drivers/hwtracing/stm/Kconfig

@@ -2,7 +2,6 @@
 config STM
 	tristate "System Trace Module devices"
 	select CONFIGFS_FS
-	select SRCU
 	help
 	  A System Trace Module (STM) is a device exporting data in System
 	  Trace Protocol (STP) format as defined by MIPI STP standards.

drivers/md/Kconfig

@@ -6,7 +6,6 @@
 menuconfig MD
 	bool "Multiple devices driver support (RAID and LVM)"
 	depends on BLOCK
-	select SRCU
 	help
 	  Support multiple physical spindles through a single logical device.
 	  Required for RAID and logical volume management.

drivers/net/Kconfig

@@ -334,7 +334,6 @@ config NETCONSOLE_DYNAMIC
 
 config NETPOLL
 	def_bool NETCONSOLE
-	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL

drivers/pci/controller/Kconfig

@@ -258,7 +258,7 @@ config PCIE_MEDIATEK_GEN3
 	  MediaTek SoCs.
 
 config VMD
-	depends on PCI_MSI && X86_64 && SRCU && !UML
+	depends on PCI_MSI && X86_64 && !UML
 	tristate "Intel Volume Management Device Driver"
 	help
 	  Adds support for the Intel Volume Management Device (VMD). VMD is a

fs/btrfs/Kconfig

@@ -17,7 +17,6 @@ config BTRFS_FS
 	select FS_IOMAP
 	select RAID6_PQ
 	select XOR_BLOCKS
-	select SRCU
 	depends on PAGE_SIZE_LESS_THAN_256KB
 
 	help

fs/locks.c

@@ -1890,7 +1890,6 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
 }
 EXPORT_SYMBOL(generic_setlease);
 
-#if IS_ENABLED(CONFIG_SRCU)
 /*
  * Kernel subsystems can register to be notified on any attempt to set
  * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
@@ -1924,30 +1923,6 @@ void lease_unregister_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(lease_unregister_notifier);
 
-#else /* !IS_ENABLED(CONFIG_SRCU) */
-static inline void
-lease_notifier_chain_init(void)
-{
-}
-
-static inline void
-setlease_notifier(long arg, struct file_lock *lease)
-{
-}
-
-int lease_register_notifier(struct notifier_block *nb)
-{
-	return 0;
-}
-EXPORT_SYMBOL_GPL(lease_register_notifier);
-
-void lease_unregister_notifier(struct notifier_block *nb)
-{
-}
-EXPORT_SYMBOL_GPL(lease_unregister_notifier);
-
-#endif /* IS_ENABLED(CONFIG_SRCU) */
-
 /**
  * vfs_setlease        -       sets a lease on an open file
  * @filp:	file pointer

fs/notify/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config FSNOTIFY
 	def_bool n
-	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"

fs/quota/Kconfig

@@ -6,7 +6,6 @@
 config QUOTA
 	bool "Quota support"
 	select QUOTACTL
-	select SRCU
 	help
 	  If you say Y here, you will be able to set per user limits for disk
 	  usage (also called disk quotas). Currently, it works for the

include/linux/kernel_stat.h

@@ -52,6 +52,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
 #define kstat_cpu(cpu) per_cpu(kstat, cpu)
 #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu)
 
+extern unsigned long long nr_context_switches_cpu(int cpu);
 extern unsigned long long nr_context_switches(void);
 
 extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu);
@@ -67,6 +68,17 @@ static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu)
        return kstat_cpu(cpu).softirqs[irq];
 }
 
+static inline unsigned int kstat_cpu_softirqs_sum(int cpu)
+{
+	int i;
+	unsigned int sum = 0;
+
+	for (i = 0; i < NR_SOFTIRQS; i++)
+		sum += kstat_softirqs_cpu(i, cpu);
+
+	return sum;
+}
+
 /*
  * Number of interrupts per specific IRQ source, since bootup
  */
@@ -75,7 +87,7 @@ extern unsigned int kstat_irqs_usr(unsigned int irq);
 /*
  * Number of interrupts per cpu, since bootup
  */
-static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
+static inline unsigned long kstat_cpu_irqs_sum(unsigned int cpu)
 {
 	return kstat_cpu(cpu).irqs_sum;
 }

include/linux/rculist_nulls.h

@@ -139,7 +139,7 @@ static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
 	if (last) {
 		n->next = last->next;
 		n->pprev = &last->next;
-		rcu_assign_pointer(hlist_next_rcu(last), n);
+		rcu_assign_pointer(hlist_nulls_next_rcu(last), n);
 	} else {
 		hlist_nulls_add_head_rcu(n, h);
 	}

include/linux/rcupdate.h

@@ -238,6 +238,7 @@ void synchronize_rcu_tasks_rude(void);
 
 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
 void exit_tasks_rcu_start(void);
+void exit_tasks_rcu_stop(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
 #define rcu_tasks_classic_qs(t, preempt) do { } while (0)
@@ -246,6 +247,7 @@ void exit_tasks_rcu_finish(void);
 #define call_rcu_tasks call_rcu
 #define synchronize_rcu_tasks synchronize_rcu
 static inline void exit_tasks_rcu_start(void) { }
+static inline void exit_tasks_rcu_stop(void) { }
 static inline void exit_tasks_rcu_finish(void) { }
 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
 
@@ -374,11 +376,18 @@ static inline int debug_lockdep_rcu_enabled(void)
  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
  * @c: condition to check
  * @s: informative message
+ *
+ * This checks debug_lockdep_rcu_enabled() before checking (c) to
+ * prevent early boot splats due to lockdep not yet being initialized,
+ * and rechecks it after checking (c) to prevent false-positive splats
+ * due to races with lockdep being disabled.  See commit 3066820034b5dd
+ * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
  */
 #define RCU_LOCKDEP_WARN(c, s)						\
 	do {								\
 		static bool __section(".data.unlikely") __warned;	\
-		if ((c) && debug_lockdep_rcu_enabled() && !__warned) {	\
+		if (debug_lockdep_rcu_enabled() && (c) &&		\
+		    debug_lockdep_rcu_enabled() && !__warned) {		\
 			__warned = true;				\
 			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
 		}							\
@@ -1004,6 +1013,9 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,		\
 	kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
 
+#define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
+#define kfree_rcu_mightsleep(ptr) kvfree_rcu_mightsleep(ptr)
+
 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
 #define kvfree_rcu_arg_2(ptr, rhf)					\
 do {									\
@@ -1011,8 +1023,7 @@ do {									\
 									\
 	if (___p) {									\
 		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));	\
-		kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)		\
-			(offsetof(typeof(*(ptr)), rhf)));				\
+		kvfree_call_rcu(&((___p)->rhf), (void *) (___p));			\
 	}										\
 } while (0)
 
@@ -1021,7 +1032,7 @@ do {								\
 	typeof(ptr) ___p = (ptr);				\
 								\
 	if (___p)						\
-		kvfree_call_rcu(NULL, (rcu_callback_t) (___p));	\
+		kvfree_call_rcu(NULL, (void *) (___p));		\
 } while (0)
 
 /*

include/linux/rcutiny.h

@@ -98,25 +98,25 @@ static inline void synchronize_rcu_expedited(void)
  */
 extern void kvfree(const void *addr);
 
-static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+static inline void __kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
 	if (head) {
-		call_rcu(head, func);
+		call_rcu(head, (rcu_callback_t) ((void *) head - ptr));
 		return;
 	}
 
 	// kvfree_rcu(one_arg) call.
 	might_sleep();
 	synchronize_rcu();
-	kvfree((void *) func);
+	kvfree(ptr);
 }
 
 #ifdef CONFIG_KASAN_GENERIC
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
+void kvfree_call_rcu(struct rcu_head *head, void *ptr);
 #else
-static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+static inline void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
-	__kvfree_call_rcu(head, func);
+	__kvfree_call_rcu(head, ptr);
 }
 #endif
 

include/linux/rcutree.h

@@ -33,7 +33,7 @@ static inline void rcu_virt_note_context_switch(void)
 }
 
 void synchronize_rcu_expedited(void);
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
+void kvfree_call_rcu(struct rcu_head *head, void *ptr);
 
 void rcu_barrier(void);
 bool rcu_eqs_special_set(int cpu);

include/linux/srcu.h

@@ -214,6 +214,34 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 	return retval;
 }
 
+/**
+ * srcu_down_read - register a new reader for an SRCU-protected structure.
+ * @ssp: srcu_struct in which to register the new reader.
+ *
+ * Enter a semaphore-like SRCU read-side critical section.  Note that
+ * SRCU read-side critical sections may be nested.  However, it is
+ * illegal to call anything that waits on an SRCU grace period for the
+ * same srcu_struct, whether directly or indirectly.  Please note that
+ * one way to indirectly wait on an SRCU grace period is to acquire
+ * a mutex that is held elsewhere while calling synchronize_srcu() or
+ * synchronize_srcu_expedited().  But if you want lockdep to help you
+ * keep this stuff straight, you should instead use srcu_read_lock().
+ *
+ * The semaphore-like nature of srcu_down_read() means that the matching
+ * srcu_up_read() can be invoked from some other context, for example,
+ * from some other task or from an irq handler.  However, neither
+ * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
+ *
+ * Calls to srcu_down_read() may be nested, similar to the manner in
+ * which calls to down_read() may be nested.
+ */
+static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
+{
+	WARN_ON_ONCE(in_nmi());
+	srcu_check_nmi_safety(ssp, false);
+	return __srcu_read_lock(ssp);
+}
+
 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
@@ -254,6 +282,23 @@ srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
 	__srcu_read_unlock(ssp, idx);
 }
 
+/**
+ * srcu_up_read - unregister a old reader from an SRCU-protected structure.
+ * @ssp: srcu_struct in which to unregister the old reader.
+ * @idx: return value from corresponding srcu_read_lock().
+ *
+ * Exit an SRCU read-side critical section, but not necessarily from
+ * the same context as the maching srcu_down_read().
+ */
+static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
+	__releases(ssp)
+{
+	WARN_ON_ONCE(idx & ~0x1);
+	WARN_ON_ONCE(in_nmi());
+	srcu_check_nmi_safety(ssp, false);
+	__srcu_read_unlock(ssp, idx);
+}
+
 /**
  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
  *

include/linux/srcutree.h

@@ -49,7 +49,7 @@ struct srcu_data {
 struct srcu_node {
 	spinlock_t __private lock;
 	unsigned long srcu_have_cbs[4];		/* GP seq for children having CBs, but only */
-						/*  if greater than ->srcu_gq_seq. */
+						/*  if greater than ->srcu_gp_seq. */
 	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs have CBs for given GP? */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	struct srcu_node *srcu_parent;		/* Next up in tree. */

init/Kconfig

@@ -1873,7 +1873,6 @@ config PERF_EVENTS
 	default y if PROFILING
 	depends on HAVE_PERF_EVENTS
 	select IRQ_WORK
-	select SRCU
 	help
 	  Enable kernel support for various performance events provided
 	  by software and hardware.

kernel/locking/locktorture.c

@@ -46,6 +46,9 @@ torture_param(int, shutdown_secs, 0, "Shutdown time (j), <= zero to disable.");
 torture_param(int, stat_interval, 60,
 	     "Number of seconds between stats printk()s");
 torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
+torture_param(int, rt_boost, 2,
+		"Do periodic rt-boost. 0=Disable, 1=Only for rt_mutex, 2=For all lock types.");
+torture_param(int, rt_boost_factor, 50, "A factor determining how often rt-boost happens.");
 torture_param(int, verbose, 1,
 	     "Enable verbose debugging printk()s");
 
@@ -127,15 +130,50 @@ static void torture_lock_busted_write_unlock(int tid __maybe_unused)
 	  /* BUGGY, do not use in real life!!! */
 }
 
-static void torture_boost_dummy(struct torture_random_state *trsp)
+static void __torture_rt_boost(struct torture_random_state *trsp)
 {
-	/* Only rtmutexes care about priority */
+	const unsigned int factor = rt_boost_factor;
+
+	if (!rt_task(current)) {
+		/*
+		 * Boost priority once every rt_boost_factor operations. When
+		 * the task tries to take the lock, the rtmutex it will account
+		 * for the new priority, and do any corresponding pi-dance.
+		 */
+		if (trsp && !(torture_random(trsp) %
+			      (cxt.nrealwriters_stress * factor))) {
+			sched_set_fifo(current);
+		} else /* common case, do nothing */
+			return;
+	} else {
+		/*
+		 * The task will remain boosted for another 10 * rt_boost_factor
+		 * operations, then restored back to its original prio, and so
+		 * forth.
+		 *
+		 * When @trsp is nil, we want to force-reset the task for
+		 * stopping the kthread.
+		 */
+		if (!trsp || !(torture_random(trsp) %
+			       (cxt.nrealwriters_stress * factor * 2))) {
+			sched_set_normal(current, 0);
+		} else /* common case, do nothing */
+			return;
+	}
+}
+
+static void torture_rt_boost(struct torture_random_state *trsp)
+{
+	if (rt_boost != 2)
+		return;
+
+	__torture_rt_boost(trsp);
 }
 
 static struct lock_torture_ops lock_busted_ops = {
 	.writelock	= torture_lock_busted_write_lock,
 	.write_delay	= torture_lock_busted_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_lock_busted_write_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -179,7 +217,7 @@ __releases(torture_spinlock)
 static struct lock_torture_ops spin_lock_ops = {
 	.writelock	= torture_spin_lock_write_lock,
 	.write_delay	= torture_spin_lock_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_spin_lock_write_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -206,7 +244,7 @@ __releases(torture_spinlock)
 static struct lock_torture_ops spin_lock_irq_ops = {
 	.writelock	= torture_spin_lock_write_lock_irq,
 	.write_delay	= torture_spin_lock_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_lock_spin_write_unlock_irq,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -275,7 +313,7 @@ __releases(torture_rwlock)
 static struct lock_torture_ops rw_lock_ops = {
 	.writelock	= torture_rwlock_write_lock,
 	.write_delay	= torture_rwlock_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_rwlock_write_unlock,
 	.readlock       = torture_rwlock_read_lock,
 	.read_delay     = torture_rwlock_read_delay,
@@ -318,7 +356,7 @@ __releases(torture_rwlock)
 static struct lock_torture_ops rw_lock_irq_ops = {
 	.writelock	= torture_rwlock_write_lock_irq,
 	.write_delay	= torture_rwlock_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_rwlock_write_unlock_irq,
 	.readlock       = torture_rwlock_read_lock_irq,
 	.read_delay     = torture_rwlock_read_delay,
@@ -358,7 +396,7 @@ __releases(torture_mutex)
 static struct lock_torture_ops mutex_lock_ops = {
 	.writelock	= torture_mutex_lock,
 	.write_delay	= torture_mutex_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_mutex_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -456,7 +494,7 @@ static struct lock_torture_ops ww_mutex_lock_ops = {
 	.exit		= torture_ww_mutex_exit,
 	.writelock	= torture_ww_mutex_lock,
 	.write_delay	= torture_mutex_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_ww_mutex_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -474,37 +512,6 @@ __acquires(torture_rtmutex)
 	return 0;
 }
 
-static void torture_rtmutex_boost(struct torture_random_state *trsp)
-{
-	const unsigned int factor = 50000; /* yes, quite arbitrary */
-
-	if (!rt_task(current)) {
-		/*
-		 * Boost priority once every ~50k operations. When the
-		 * task tries to take the lock, the rtmutex it will account
-		 * for the new priority, and do any corresponding pi-dance.
-		 */
-		if (trsp && !(torture_random(trsp) %
-			      (cxt.nrealwriters_stress * factor))) {
-			sched_set_fifo(current);
-		} else /* common case, do nothing */
-			return;
-	} else {
-		/*
-		 * The task will remain boosted for another ~500k operations,
-		 * then restored back to its original prio, and so forth.
-		 *
-		 * When @trsp is nil, we want to force-reset the task for
-		 * stopping the kthread.
-		 */
-		if (!trsp || !(torture_random(trsp) %
-			       (cxt.nrealwriters_stress * factor * 2))) {
-			sched_set_normal(current, 0);
-		} else /* common case, do nothing */
-			return;
-	}
-}
-
 static void torture_rtmutex_delay(struct torture_random_state *trsp)
 {
 	const unsigned long shortdelay_us = 2;
@@ -530,10 +537,18 @@ __releases(torture_rtmutex)
 	rt_mutex_unlock(&torture_rtmutex);
 }
 
+static void torture_rt_boost_rtmutex(struct torture_random_state *trsp)
+{
+	if (!rt_boost)
+		return;
+
+	__torture_rt_boost(trsp);
+}
+
 static struct lock_torture_ops rtmutex_lock_ops = {
 	.writelock	= torture_rtmutex_lock,
 	.write_delay	= torture_rtmutex_delay,
-	.task_boost     = torture_rtmutex_boost,
+	.task_boost     = torture_rt_boost_rtmutex,
 	.writeunlock	= torture_rtmutex_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
@@ -600,7 +615,7 @@ __releases(torture_rwsem)
 static struct lock_torture_ops rwsem_lock_ops = {
 	.writelock	= torture_rwsem_down_write,
 	.write_delay	= torture_rwsem_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_rwsem_up_write,
 	.readlock       = torture_rwsem_down_read,
 	.read_delay     = torture_rwsem_read_delay,
@@ -652,7 +667,7 @@ static struct lock_torture_ops percpu_rwsem_lock_ops = {
 	.exit		= torture_percpu_rwsem_exit,
 	.writelock	= torture_percpu_rwsem_down_write,
 	.write_delay	= torture_rwsem_write_delay,
-	.task_boost     = torture_boost_dummy,
+	.task_boost     = torture_rt_boost,
 	.writeunlock	= torture_percpu_rwsem_up_write,
 	.readlock       = torture_percpu_rwsem_down_read,
 	.read_delay     = torture_rwsem_read_delay,

kernel/notifier.c

@@ -456,7 +456,6 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
-#ifdef CONFIG_SRCU
 /*
  *	SRCU notifier chain routines.    Registration and unregistration
  *	use a mutex, and call_chain is synchronized by SRCU (no locks).
@@ -573,8 +572,6 @@ void srcu_init_notifier_head(struct srcu_notifier_head *nh)
 }
 EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
 
-#endif /* CONFIG_SRCU */
-
 static ATOMIC_NOTIFIER_HEAD(die_chain);
 
 int notrace notify_die(enum die_val val, const char *str,

kernel/pid_namespace.c

@@ -244,7 +244,24 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (pid_ns->pid_allocated == init_pids)
 			break;
+		/*
+		 * Release tasks_rcu_exit_srcu to avoid following deadlock:
+		 *
+		 * 1) TASK A unshare(CLONE_NEWPID)
+		 * 2) TASK A fork() twice -> TASK B (child reaper for new ns)
+		 *    and TASK C
+		 * 3) TASK B exits, kills TASK C, waits for TASK A to reap it
+		 * 4) TASK A calls synchronize_rcu_tasks()
+		 *                   -> synchronize_srcu(tasks_rcu_exit_srcu)
+		 * 5) *DEADLOCK*
+		 *
+		 * It is considered safe to release tasks_rcu_exit_srcu here
+		 * because we assume the current task can not be concurrently
+		 * reaped at this point.
+		 */
+		exit_tasks_rcu_stop();
 		schedule();
+		exit_tasks_rcu_start();
 	}
 	__set_current_state(TASK_RUNNING);
 

kernel/rcu/Kconfig.debug

@@ -82,7 +82,7 @@ config RCU_CPU_STALL_TIMEOUT
 config RCU_EXP_CPU_STALL_TIMEOUT
 	int "Expedited RCU CPU stall timeout in milliseconds"
 	depends on RCU_STALL_COMMON
-	range 0 21000
+	range 0 300000
 	default 0
 	help
 	  If a given expedited RCU grace period extends more than the
@@ -92,6 +92,19 @@ config RCU_EXP_CPU_STALL_TIMEOUT
 	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
 	  seconds to milliseconds.
 
+config RCU_CPU_STALL_CPUTIME
+	bool "Provide additional RCU stall debug information"
+	depends on RCU_STALL_COMMON
+	default n
+	help
+	  Collect statistics during the sampling period, such as the number of
+	  (hard interrupts, soft interrupts, task switches) and the cputime of
+	  (hard interrupts, soft interrupts, kernel tasks) are added to the
+	  RCU stall report. For multiple continuous RCU stalls, all sampling
+	  periods begin at half of the first RCU stall timeout.
+	  The boot option rcupdate.rcu_cpu_stall_cputime has the same function
+	  as this one, but will override this if it exists.
+
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL

kernel/rcu/rcu.h

@@ -224,6 +224,8 @@ extern int rcu_cpu_stall_ftrace_dump;
 extern int rcu_cpu_stall_suppress;
 extern int rcu_cpu_stall_timeout;
 extern int rcu_exp_cpu_stall_timeout;
+extern int rcu_cpu_stall_cputime;
+extern bool rcu_exp_stall_task_details __read_mostly;
 int rcu_jiffies_till_stall_check(void);
 int rcu_exp_jiffies_till_stall_check(void);
 
@@ -447,14 +449,20 @@ do {									\
 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
 static inline bool rcu_gp_is_normal(void) { return true; }
 static inline bool rcu_gp_is_expedited(void) { return false; }
+static inline bool rcu_async_should_hurry(void) { return false; }
 static inline void rcu_expedite_gp(void) { }
 static inline void rcu_unexpedite_gp(void) { }
+static inline void rcu_async_hurry(void) { }
+static inline void rcu_async_relax(void) { }
 static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
 #else /* #ifdef CONFIG_TINY_RCU */
 bool rcu_gp_is_normal(void);     /* Internal RCU use. */
 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
+bool rcu_async_should_hurry(void);  /* Internal RCU use. */
 void rcu_expedite_gp(void);
 void rcu_unexpedite_gp(void);
+void rcu_async_hurry(void);
+void rcu_async_relax(void);
 void rcupdate_announce_bootup_oddness(void);
 #ifdef CONFIG_TASKS_RCU_GENERIC
 void show_rcu_tasks_gp_kthreads(void);

kernel/rcu/rcu_segcblist.c

@@ -89,7 +89,7 @@ static void rcu_segcblist_set_len(struct rcu_segcblist *rsclp, long v)
 }
 
 /* Get the length of a segment of the rcu_segcblist structure. */
-static long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg)
+long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg)
 {
 	return READ_ONCE(rsclp->seglen[seg]);
 }

kernel/rcu/rcu_segcblist.h

@@ -15,6 +15,8 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
 	return READ_ONCE(rclp->len);
 }
 
+long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg);
+
 /* Return number of callbacks in segmented callback list by summing seglen. */
 long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp);
 

kernel/rcu/rcutorture.c

@@ -399,7 +399,7 @@ static int torture_readlock_not_held(void)
 	return rcu_read_lock_bh_held() || rcu_read_lock_sched_held();
 }
 
-static int rcu_torture_read_lock(void) __acquires(RCU)
+static int rcu_torture_read_lock(void)
 {
 	rcu_read_lock();
 	return 0;
@@ -441,7 +441,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
 	}
 }
 
-static void rcu_torture_read_unlock(int idx) __releases(RCU)
+static void rcu_torture_read_unlock(int idx)
 {
 	rcu_read_unlock();
 }
@@ -625,7 +625,7 @@ static struct srcu_struct srcu_ctld;
 static struct srcu_struct *srcu_ctlp = &srcu_ctl;
 static struct rcu_torture_ops srcud_ops;
 
-static int srcu_torture_read_lock(void) __acquires(srcu_ctlp)
+static int srcu_torture_read_lock(void)
 {
 	if (cur_ops == &srcud_ops)
 		return srcu_read_lock_nmisafe(srcu_ctlp);
@@ -652,7 +652,7 @@ srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
 	}
 }
 
-static void srcu_torture_read_unlock(int idx) __releases(srcu_ctlp)
+static void srcu_torture_read_unlock(int idx)
 {
 	if (cur_ops == &srcud_ops)
 		srcu_read_unlock_nmisafe(srcu_ctlp, idx);
@@ -814,13 +814,13 @@ static void synchronize_rcu_trivial(void)
 	}
 }
 
-static int rcu_torture_read_lock_trivial(void) __acquires(RCU)
+static int rcu_torture_read_lock_trivial(void)
 {
 	preempt_disable();
 	return 0;
 }
 
-static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU)
+static void rcu_torture_read_unlock_trivial(int idx)
 {
 	preempt_enable();
 }

kernel/rcu/refscale.c

@@ -76,6 +76,8 @@ torture_param(int, verbose_batched, 0, "Batch verbose debugging printk()s");
 // Wait until there are multiple CPUs before starting test.
 torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0,
 	      "Holdoff time before test start (s)");
+// Number of typesafe_lookup structures, that is, the degree of concurrency.
+torture_param(long, lookup_instances, 0, "Number of typesafe_lookup structures.");
 // Number of loops per experiment, all readers execute operations concurrently.
 torture_param(long, loops, 10000, "Number of loops per experiment.");
 // Number of readers, with -1 defaulting to about 75% of the CPUs.
@@ -124,7 +126,7 @@ static int exp_idx;
 
 // Operations vector for selecting different types of tests.
 struct ref_scale_ops {
-	void (*init)(void);
+	bool (*init)(void);
 	void (*cleanup)(void);
 	void (*readsection)(const int nloops);
 	void (*delaysection)(const int nloops, const int udl, const int ndl);
@@ -162,8 +164,9 @@ static void ref_rcu_delay_section(const int nloops, const int udl, const int ndl
 	}
 }
 
-static void rcu_sync_scale_init(void)
+static bool rcu_sync_scale_init(void)
 {
+	return true;
 }
 
 static struct ref_scale_ops rcu_ops = {
@@ -315,9 +318,10 @@ static struct ref_scale_ops refcnt_ops = {
 // Definitions for rwlock
 static rwlock_t test_rwlock;
 
-static void ref_rwlock_init(void)
+static bool ref_rwlock_init(void)
 {
 	rwlock_init(&test_rwlock);
+	return true;
 }
 
 static void ref_rwlock_section(const int nloops)
@@ -351,9 +355,10 @@ static struct ref_scale_ops rwlock_ops = {
 // Definitions for rwsem
 static struct rw_semaphore test_rwsem;
 
-static void ref_rwsem_init(void)
+static bool ref_rwsem_init(void)
 {
 	init_rwsem(&test_rwsem);
+	return true;
 }
 
 static void ref_rwsem_section(const int nloops)
@@ -523,6 +528,237 @@ static struct ref_scale_ops clock_ops = {
 	.name		= "clock"
 };
 
+////////////////////////////////////////////////////////////////////////
+//
+// Methods leveraging SLAB_TYPESAFE_BY_RCU.
+//
+
+// Item to look up in a typesafe manner.  Array of pointers to these.
+struct refscale_typesafe {
+	atomic_t rts_refctr;  // Used by all flavors
+	spinlock_t rts_lock;
+	seqlock_t rts_seqlock;
+	unsigned int a;
+	unsigned int b;
+};
+
+static struct kmem_cache *typesafe_kmem_cachep;
+static struct refscale_typesafe **rtsarray;
+static long rtsarray_size;
+static DEFINE_TORTURE_RANDOM_PERCPU(refscale_rand);
+static bool (*rts_acquire)(struct refscale_typesafe *rtsp, unsigned int *start);
+static bool (*rts_release)(struct refscale_typesafe *rtsp, unsigned int start);
+
+// Conditionally acquire an explicit in-structure reference count.
+static bool typesafe_ref_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
+{
+	return atomic_inc_not_zero(&rtsp->rts_refctr);
+}
+
+// Unconditionally release an explicit in-structure reference count.
+static bool typesafe_ref_release(struct refscale_typesafe *rtsp, unsigned int start)
+{
+	if (!atomic_dec_return(&rtsp->rts_refctr)) {
+		WRITE_ONCE(rtsp->a, rtsp->a + 1);
+		kmem_cache_free(typesafe_kmem_cachep, rtsp);
+	}
+	return true;
+}
+
+// Unconditionally acquire an explicit in-structure spinlock.
+static bool typesafe_lock_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
+{
+	spin_lock(&rtsp->rts_lock);
+	return true;
+}
+
+// Unconditionally release an explicit in-structure spinlock.
+static bool typesafe_lock_release(struct refscale_typesafe *rtsp, unsigned int start)
+{
+	spin_unlock(&rtsp->rts_lock);
+	return true;
+}
+
+// Unconditionally acquire an explicit in-structure sequence lock.
+static bool typesafe_seqlock_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
+{
+	*start = read_seqbegin(&rtsp->rts_seqlock);
+	return true;
+}
+
+// Conditionally release an explicit in-structure sequence lock.  Return
+// true if this release was successful, that is, if no retry is required.
+static bool typesafe_seqlock_release(struct refscale_typesafe *rtsp, unsigned int start)
+{
+	return !read_seqretry(&rtsp->rts_seqlock, start);
+}
+
+// Do a read-side critical section with the specified delay in
+// microseconds and nanoseconds inserted so as to increase probability
+// of failure.
+static void typesafe_delay_section(const int nloops, const int udl, const int ndl)
+{
+	unsigned int a;
+	unsigned int b;
+	int i;
+	long idx;
+	struct refscale_typesafe *rtsp;
+	unsigned int start;
+
+	for (i = nloops; i >= 0; i--) {
+		preempt_disable();
+		idx = torture_random(this_cpu_ptr(&refscale_rand)) % rtsarray_size;
+		preempt_enable();
+retry:
+		rcu_read_lock();
+		rtsp = rcu_dereference(rtsarray[idx]);
+		a = READ_ONCE(rtsp->a);
+		if (!rts_acquire(rtsp, &start)) {
+			rcu_read_unlock();
+			goto retry;
+		}
+		if (a != READ_ONCE(rtsp->a)) {
+			(void)rts_release(rtsp, start);
+			rcu_read_unlock();
+			goto retry;
+		}
+		un_delay(udl, ndl);
+		// Remember, seqlock read-side release can fail.
+		if (!rts_release(rtsp, start)) {
+			rcu_read_unlock();
+			goto retry;
+		}
+		b = READ_ONCE(rtsp->a);
+		WARN_ONCE(a != b, "Re-read of ->a changed from %u to %u.\n", a, b);
+		b = rtsp->b;
+		rcu_read_unlock();
+		WARN_ON_ONCE(a * a != b);
+	}
+}
+
+// Because the acquisition and release methods are expensive, there
+// is no point in optimizing away the un_delay() function's two checks.
+// Thus simply define typesafe_read_section() as a simple wrapper around
+// typesafe_delay_section().
+static void typesafe_read_section(const int nloops)
+{
+	typesafe_delay_section(nloops, 0, 0);
+}
+
+// Allocate and initialize one refscale_typesafe structure.
+static struct refscale_typesafe *typesafe_alloc_one(void)
+{
+	struct refscale_typesafe *rtsp;
+
+	rtsp = kmem_cache_alloc(typesafe_kmem_cachep, GFP_KERNEL);
+	if (!rtsp)
+		return NULL;
+	atomic_set(&rtsp->rts_refctr, 1);
+	WRITE_ONCE(rtsp->a, rtsp->a + 1);
+	WRITE_ONCE(rtsp->b, rtsp->a * rtsp->a);
+	return rtsp;
+}
+
+// Slab-allocator constructor for refscale_typesafe structures created
+// out of a new slab of system memory.
+static void refscale_typesafe_ctor(void *rtsp_in)
+{
+	struct refscale_typesafe *rtsp = rtsp_in;
+
+	spin_lock_init(&rtsp->rts_lock);
+	seqlock_init(&rtsp->rts_seqlock);
+	preempt_disable();
+	rtsp->a = torture_random(this_cpu_ptr(&refscale_rand));
+	preempt_enable();
+}
+
+static struct ref_scale_ops typesafe_ref_ops;
+static struct ref_scale_ops typesafe_lock_ops;
+static struct ref_scale_ops typesafe_seqlock_ops;
+
+// Initialize for a typesafe test.
+static bool typesafe_init(void)
+{
+	long idx;
+	long si = lookup_instances;
+
+	typesafe_kmem_cachep = kmem_cache_create("refscale_typesafe",
+						 sizeof(struct refscale_typesafe), sizeof(void *),
+						 SLAB_TYPESAFE_BY_RCU, refscale_typesafe_ctor);
+	if (!typesafe_kmem_cachep)
+		return false;
+	if (si < 0)
+		si = -si * nr_cpu_ids;
+	else if (si == 0)
+		si = nr_cpu_ids;
+	rtsarray_size = si;
+	rtsarray = kcalloc(si, sizeof(*rtsarray), GFP_KERNEL);
+	if (!rtsarray)
+		return false;
+	for (idx = 0; idx < rtsarray_size; idx++) {
+		rtsarray[idx] = typesafe_alloc_one();
+		if (!rtsarray[idx])
+			return false;
+	}
+	if (cur_ops == &typesafe_ref_ops) {
+		rts_acquire = typesafe_ref_acquire;
+		rts_release = typesafe_ref_release;
+	} else if (cur_ops == &typesafe_lock_ops) {
+		rts_acquire = typesafe_lock_acquire;
+		rts_release = typesafe_lock_release;
+	} else if (cur_ops == &typesafe_seqlock_ops) {
+		rts_acquire = typesafe_seqlock_acquire;
+		rts_release = typesafe_seqlock_release;
+	} else {
+		WARN_ON_ONCE(1);
+		return false;
+	}
+	return true;
+}
+
+// Clean up after a typesafe test.
+static void typesafe_cleanup(void)
+{
+	long idx;
+
+	if (rtsarray) {
+		for (idx = 0; idx < rtsarray_size; idx++)
+			kmem_cache_free(typesafe_kmem_cachep, rtsarray[idx]);
+		kfree(rtsarray);
+		rtsarray = NULL;
+		rtsarray_size = 0;
+	}
+	kmem_cache_destroy(typesafe_kmem_cachep);
+	typesafe_kmem_cachep = NULL;
+	rts_acquire = NULL;
+	rts_release = NULL;
+}
+
+// The typesafe_init() function distinguishes these structures by address.
+static struct ref_scale_ops typesafe_ref_ops = {
+	.init		= typesafe_init,
+	.cleanup	= typesafe_cleanup,
+	.readsection	= typesafe_read_section,
+	.delaysection	= typesafe_delay_section,
+	.name		= "typesafe_ref"
+};
+
+static struct ref_scale_ops typesafe_lock_ops = {
+	.init		= typesafe_init,
+	.cleanup	= typesafe_cleanup,
+	.readsection	= typesafe_read_section,
+	.delaysection	= typesafe_delay_section,
+	.name		= "typesafe_lock"
+};
+
+static struct ref_scale_ops typesafe_seqlock_ops = {
+	.init		= typesafe_init,
+	.cleanup	= typesafe_cleanup,
+	.readsection	= typesafe_read_section,
+	.delaysection	= typesafe_delay_section,
+	.name		= "typesafe_seqlock"
+};
+
 static void rcu_scale_one_reader(void)
 {
 	if (readdelay <= 0)
@@ -812,6 +1048,7 @@ ref_scale_init(void)
 	static struct ref_scale_ops *scale_ops[] = {
 		&rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
 		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
+		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
 	};
 
 	if (!torture_init_begin(scale_type, verbose))
@@ -833,7 +1070,10 @@ ref_scale_init(void)
 		goto unwind;
 	}
 	if (cur_ops->init)
-		cur_ops->init();
+		if (!cur_ops->init()) {
+			firsterr = -EUCLEAN;
+			goto unwind;
+		}
 
 	ref_scale_print_module_parms(cur_ops, "Start of test");
 

kernel/rcu/srcutree.c

@@ -154,7 +154,7 @@ static void init_srcu_struct_data(struct srcu_struct *ssp)
  */
 static inline bool srcu_invl_snp_seq(unsigned long s)
 {
-	return rcu_seq_state(s) == SRCU_SNP_INIT_SEQ;
+	return s == SRCU_SNP_INIT_SEQ;
 }
 
 /*
@@ -469,24 +469,59 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
 
 	/*
 	 * If the locks are the same as the unlocks, then there must have
-	 * been no readers on this index at some time in between. This does
-	 * not mean that there are no more readers, as one could have read
-	 * the current index but not have incremented the lock counter yet.
+	 * been no readers on this index at some point in this function.
+	 * But there might be more readers, as a task might have read
+	 * the current ->srcu_idx but not yet have incremented its CPU's
+	 * ->srcu_lock_count[idx] counter.  In fact, it is possible
+	 * that most of the tasks have been preempted between fetching
+	 * ->srcu_idx and incrementing ->srcu_lock_count[idx].  And there
+	 * could be almost (ULONG_MAX / sizeof(struct task_struct)) tasks
+	 * in a system whose address space was fully populated with memory.
+	 * Call this quantity Nt.
 	 *
-	 * So suppose that the updater is preempted here for so long
-	 * that more than ULONG_MAX non-nested readers come and go in
-	 * the meantime.  It turns out that this cannot result in overflow
-	 * because if a reader modifies its unlock count after we read it
-	 * above, then that reader's next load of ->srcu_idx is guaranteed
-	 * to get the new value, which will cause it to operate on the
-	 * other bank of counters, where it cannot contribute to the
-	 * overflow of these counters.  This means that there is a maximum
-	 * of 2*NR_CPUS increments, which cannot overflow given current
-	 * systems, especially not on 64-bit systems.
+	 * So suppose that the updater is preempted at this point in the
+	 * code for a long time.  That now-preempted updater has already
+	 * flipped ->srcu_idx (possibly during the preceding grace period),
+	 * done an smp_mb() (again, possibly during the preceding grace
+	 * period), and summed up the ->srcu_unlock_count[idx] counters.
+	 * How many times can a given one of the aforementioned Nt tasks
+	 * increment the old ->srcu_idx value's ->srcu_lock_count[idx]
+	 * counter, in the absence of nesting?
 	 *
-	 * OK, how about nesting?  This does impose a limit on nesting
-	 * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient,
-	 * especially on 64-bit systems.
+	 * It can clearly do so once, given that it has already fetched
+	 * the old value of ->srcu_idx and is just about to use that value
+	 * to index its increment of ->srcu_lock_count[idx].  But as soon as
+	 * it leaves that SRCU read-side critical section, it will increment
+	 * ->srcu_unlock_count[idx], which must follow the updater's above
+	 * read from that same value.  Thus, as soon the reading task does
+	 * an smp_mb() and a later fetch from ->srcu_idx, that task will be
+	 * guaranteed to get the new index.  Except that the increment of
+	 * ->srcu_unlock_count[idx] in __srcu_read_unlock() is after the
+	 * smp_mb(), and the fetch from ->srcu_idx in __srcu_read_lock()
+	 * is before the smp_mb().  Thus, that task might not see the new
+	 * value of ->srcu_idx until the -second- __srcu_read_lock(),
+	 * which in turn means that this task might well increment
+	 * ->srcu_lock_count[idx] for the old value of ->srcu_idx twice,
+	 * not just once.
+	 *
+	 * However, it is important to note that a given smp_mb() takes
+	 * effect not just for the task executing it, but also for any
+	 * later task running on that same CPU.
+	 *
+	 * That is, there can be almost Nt + Nc further increments of
+	 * ->srcu_lock_count[idx] for the old index, where Nc is the number
+	 * of CPUs.  But this is OK because the size of the task_struct
+	 * structure limits the value of Nt and current systems limit Nc
+	 * to a few thousand.
+	 *
+	 * OK, but what about nesting?  This does impose a limit on
+	 * nesting of half of the size of the task_struct structure
+	 * (measured in bytes), which should be sufficient.  A late 2022
+	 * TREE01 rcutorture run reported this size to be no less than
+	 * 9408 bytes, allowing up to 4704 levels of nesting, which is
+	 * comfortably beyond excessive.  Especially on 64-bit systems,
+	 * which are unlikely to be configured with an address space fully
+	 * populated with memory, at least not anytime soon.
 	 */
 	return srcu_readers_lock_idx(ssp, idx) == unlocks;
 }
@@ -726,7 +761,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
 	int state;
 
 	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
-		sdp = per_cpu_ptr(ssp->sda, 0);
+		sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
 	else
 		sdp = this_cpu_ptr(ssp->sda);
 	lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
@@ -837,7 +872,8 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	/* Initiate callback invocation as needed. */
 	ss_state = smp_load_acquire(&ssp->srcu_size_state);
 	if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
-		srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, 0), cbdelay);
+		srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()),
+					cbdelay);
 	} else {
 		idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
 		srcu_for_each_node_breadth_first(ssp, snp) {
@@ -914,7 +950,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
 	if (snp)
 		for (; snp != NULL; snp = snp->srcu_parent) {
 			sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp);
-			if (rcu_seq_done(&ssp->srcu_gp_seq, s) ||
+			if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) ||
 			    (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)))
 				return;
 			spin_lock_irqsave_rcu_node(snp, flags);
@@ -941,6 +977,9 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
  *
  * Note that this function also does the work of srcu_funnel_exp_start(),
  * in some cases by directly invoking it.
+ *
+ * The srcu read lock should be hold around this function. And s is a seq snap
+ * after holding that lock.
  */
 static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 				 unsigned long s, bool do_norm)
@@ -961,7 +1000,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 	if (snp_leaf)
 		/* Each pass through the loop does one level of the srcu_node tree. */
 		for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
-			if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != snp_leaf)
+			if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) && snp != snp_leaf)
 				return; /* GP already done and CBs recorded. */
 			spin_lock_irqsave_rcu_node(snp, flags);
 			snp_seq = snp->srcu_have_cbs[idx];
@@ -998,8 +1037,8 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 	if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
 		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
 
-	/* If grace period not already done and none in progress, start it. */
-	if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&
+	/* If grace period not already in progress, start it. */
+	if (!WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) &&
 	    rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
 		WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
 		srcu_gp_start(ssp);
@@ -1059,10 +1098,11 @@ static void srcu_flip(struct srcu_struct *ssp)
 
 	/*
 	 * Ensure that if the updater misses an __srcu_read_unlock()
-	 * increment, that task's next __srcu_read_lock() will see the
-	 * above counter update.  Note that both this memory barrier
-	 * and the one in srcu_readers_active_idx_check() provide the
-	 * guarantee for __srcu_read_lock().
+	 * increment, that task's __srcu_read_lock() following its next
+	 * __srcu_read_lock() or __srcu_read_unlock() will see the above
+	 * counter update.  Note that both this memory barrier and the
+	 * one in srcu_readers_active_idx_check() provide the guarantee
+	 * for __srcu_read_lock().
 	 */
 	smp_mb(); /* D */  /* Pairs with C. */
 }
@@ -1161,7 +1201,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	idx = __srcu_read_lock_nmisafe(ssp);
 	ss_state = smp_load_acquire(&ssp->srcu_size_state);
 	if (ss_state < SRCU_SIZE_WAIT_CALL)
-		sdp = per_cpu_ptr(ssp->sda, 0);
+		sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
 	else
 		sdp = raw_cpu_ptr(ssp->sda);
 	spin_lock_irqsave_sdp_contention(sdp, &flags);
@@ -1497,7 +1537,7 @@ void srcu_barrier(struct srcu_struct *ssp)
 
 	idx = __srcu_read_lock_nmisafe(ssp);
 	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
-		srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
+		srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda,	get_boot_cpu_id()));
 	else
 		for_each_possible_cpu(cpu)
 			srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));

kernel/rcu/tasks.h

@@ -384,6 +384,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
 {
 	int cpu;
 	unsigned long flags;
+	bool gpdone = poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq);
 	long n;
 	long ncbs = 0;
 	long ncbsnz = 0;
@@ -425,21 +426,23 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
 			WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids));
 			smp_store_release(&rtp->percpu_enqueue_lim, 1);
 			rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu();
+			gpdone = false;
 			pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name);
 		}
 		raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
 	}
-	if (rcu_task_cb_adjust && !ncbsnz &&
-	    poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq)) {
+	if (rcu_task_cb_adjust && !ncbsnz && gpdone) {
 		raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
 		if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) {
 			WRITE_ONCE(rtp->percpu_dequeue_lim, 1);
 			pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name);
 		}
-		for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) {
-			struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
+		if (rtp->percpu_dequeue_lim == 1) {
+			for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) {
+				struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
 
-			WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist));
+				WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist));
+			}
 		}
 		raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
 	}
@@ -560,8 +563,9 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
 {
 	/* Complain if the scheduler has not started.  */
-	WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
-			 "synchronize_rcu_tasks called too soon");
+	if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
+			 "synchronize_%s() called too soon", rtp->name))
+		return;
 
 	// If the grace-period kthread is running, use it.
 	if (READ_ONCE(rtp->kthread_ptr)) {
@@ -827,11 +831,21 @@ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
 static void rcu_tasks_postscan(struct list_head *hop)
 {
 	/*
-	 * Wait for tasks that are in the process of exiting.  This
-	 * does only part of the job, ensuring that all tasks that were
-	 * previously exiting reach the point where they have disabled
-	 * preemption, allowing the later synchronize_rcu() to finish
-	 * the job.
+	 * Exiting tasks may escape the tasklist scan. Those are vulnerable
+	 * until their final schedule() with TASK_DEAD state. To cope with
+	 * this, divide the fragile exit path part in two intersecting
+	 * read side critical sections:
+	 *
+	 * 1) An _SRCU_ read side starting before calling exit_notify(),
+	 *    which may remove the task from the tasklist, and ending after
+	 *    the final preempt_disable() call in do_exit().
+	 *
+	 * 2) An _RCU_ read side starting with the final preempt_disable()
+	 *    call in do_exit() and ending with the final call to schedule()
+	 *    with TASK_DEAD state.
+	 *
+	 * This handles the part 1). And postgp will handle part 2) with a
+	 * call to synchronize_rcu().
 	 */
 	synchronize_srcu(&tasks_rcu_exit_srcu);
 }
@@ -898,7 +912,10 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp)
 	 *
 	 * In addition, this synchronize_rcu() waits for exiting tasks
 	 * to complete their final preempt_disable() region of execution,
-	 * cleaning up after the synchronize_srcu() above.
+	 * cleaning up after synchronize_srcu(&tasks_rcu_exit_srcu),
+	 * enforcing the whole region before tasklist removal until
+	 * the final schedule() with TASK_DEAD state to be an RCU TASKS
+	 * read side critical section.
 	 */
 	synchronize_rcu();
 }
@@ -988,27 +1005,42 @@ void show_rcu_tasks_classic_gp_kthread(void)
 EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread);
 #endif // !defined(CONFIG_TINY_RCU)
 
-/* Do the srcu_read_lock() for the above synchronize_srcu().  */
+/*
+ * Contribute to protect against tasklist scan blind spot while the
+ * task is exiting and may be removed from the tasklist. See
+ * corresponding synchronize_srcu() for further details.
+ */
 void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
 {
-	preempt_disable();
 	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
-	preempt_enable();
 }
 
-/* Do the srcu_read_unlock() for the above synchronize_srcu().  */
-void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
+/*
+ * Contribute to protect against tasklist scan blind spot while the
+ * task is exiting and may be removed from the tasklist. See
+ * corresponding synchronize_srcu() for further details.
+ */
+void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu)
 {
 	struct task_struct *t = current;
 
-	preempt_disable();
 	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
-	preempt_enable();
-	exit_tasks_rcu_finish_trace(t);
+}
+
+/*
+ * Contribute to protect against tasklist scan blind spot while the
+ * task is exiting and may be removed from the tasklist. See
+ * corresponding synchronize_srcu() for further details.
+ */
+void exit_tasks_rcu_finish(void)
+{
+	exit_tasks_rcu_stop();
+	exit_tasks_rcu_finish_trace(current);
 }
 
 #else /* #ifdef CONFIG_TASKS_RCU */
 void exit_tasks_rcu_start(void) { }
+void exit_tasks_rcu_stop(void) { }
 void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); }
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
@@ -1036,9 +1068,6 @@ static void rcu_tasks_be_rude(struct work_struct *work)
 // Wait for one rude RCU-tasks grace period.
 static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
 {
-	if (num_online_cpus() <= 1)
-		return;	// Fastpath for only one CPU.
-
 	rtp->n_ipis += cpumask_weight(cpu_online_mask);
 	schedule_on_each_cpu(rcu_tasks_be_rude);
 }
@@ -1815,23 +1844,21 @@ static void test_rcu_tasks_callback(struct rcu_head *rhp)
 
 static void rcu_tasks_initiate_self_tests(void)
 {
-	unsigned long j = jiffies;
-
 	pr_info("Running RCU-tasks wait API self tests\n");
 #ifdef CONFIG_TASKS_RCU
-	tests[0].runstart = j;
+	tests[0].runstart = jiffies;
 	synchronize_rcu_tasks();
 	call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
 #endif
 
 #ifdef CONFIG_TASKS_RUDE_RCU
-	tests[1].runstart = j;
+	tests[1].runstart = jiffies;
 	synchronize_rcu_tasks_rude();
 	call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
 #endif
 
 #ifdef CONFIG_TASKS_TRACE_RCU
-	tests[2].runstart = j;
+	tests[2].runstart = jiffies;
 	synchronize_rcu_tasks_trace();
 	call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
 #endif

kernel/rcu/tiny.c

@@ -246,15 +246,12 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 
 #ifdef CONFIG_KASAN_GENERIC
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
-	if (head) {
-		void *ptr = (void *) head - (unsigned long) func;
-
+	if (head)
 		kasan_record_aux_stack_noalloc(ptr);
-	}
 
-	__kvfree_call_rcu(head, func);
+	__kvfree_call_rcu(head, ptr);
 }
 EXPORT_SYMBOL_GPL(kvfree_call_rcu);
 #endif

kernel/rcu/tree.h

@@ -158,6 +158,23 @@ union rcu_noqs {
 	u16 s; /* Set of bits, aggregate OR here. */
 };
 
+/*
+ * Record the snapshot of the core stats at half of the first RCU stall timeout.
+ * The member gp_seq is used to ensure that all members are updated only once
+ * during the sampling period. The snapshot is taken only if this gp_seq is not
+ * equal to rdp->gp_seq.
+ */
+struct rcu_snap_record {
+	unsigned long	gp_seq;		/* Track rdp->gp_seq counter */
+	u64		cputime_irq;	/* Accumulated cputime of hard irqs */
+	u64		cputime_softirq;/* Accumulated cputime of soft irqs */
+	u64		cputime_system; /* Accumulated cputime of kernel tasks */
+	unsigned long	nr_hardirqs;	/* Accumulated number of hard irqs */
+	unsigned int	nr_softirqs;	/* Accumulated number of soft irqs */
+	unsigned long long nr_csw;	/* Accumulated number of task switches */
+	unsigned long   jiffies;	/* Track jiffies value */
+};
+
 /* Per-CPU data for read-copy update. */
 struct rcu_data {
 	/* 1) quiescent-state and grace-period handling : */
@@ -262,6 +279,8 @@ struct rcu_data {
 	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */
 	unsigned long last_fqs_resched;	/* Time of last rcu_resched(). */
 	unsigned long last_sched_clock;	/* Jiffies of last rcu_sched_clock_irq(). */
+	struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */
+					    /* the first RCU stall timeout */
 
 	long lazy_len;			/* Length of buffered lazy callbacks. */
 	int cpu;

kernel/rcu/tree_exp.h

@@ -11,6 +11,7 @@
 
 static void rcu_exp_handler(void *unused);
 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
+static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
 
 /*
  * Record the start of an expedited grace period.
@@ -667,8 +668,11 @@ static void synchronize_rcu_expedited_wait(void)
 				mask = leaf_node_cpu_bit(rnp, cpu);
 				if (!(READ_ONCE(rnp->expmask) & mask))
 					continue;
+				preempt_disable(); // For smp_processor_id() in dump_cpu_task().
 				dump_cpu_task(cpu);
+				preempt_enable();
 			}
+			rcu_exp_print_detail_task_stall_rnp(rnp);
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
 		panic_on_rcu_stall();
@@ -811,6 +815,36 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 	return ndetected;
 }
 
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, dumping the stack of each that is blocking the current
+ * expedited grace period.
+ */
+static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	struct task_struct *t;
+
+	if (!rcu_exp_stall_task_details)
+		return;
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	if (!READ_ONCE(rnp->exp_tasks)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	t = list_entry(rnp->exp_tasks->prev,
+		       struct task_struct, rcu_node_entry);
+	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+		/*
+		 * We could be printing a lot while holding a spinlock.
+		 * Avoid triggering hard lockup.
+		 */
+		touch_nmi_watchdog();
+		sched_show_task(t);
+	}
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 /* Request an expedited quiescent state. */
@@ -883,6 +917,15 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 	return 0;
 }
 
+/*
+ * Because preemptible RCU does not exist, we never have to print out
+ * tasks blocked within RCU read-side critical sections that are blocking
+ * the current expedited grace period.
+ */
+static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+}
+
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /**

kernel/rcu/tree_stall.h

@@ -39,7 +39,7 @@ int rcu_exp_jiffies_till_stall_check(void)
 	// CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
 	// The minimum clamped value is "2UL", because at least one full
 	// tick has to be guaranteed.
-	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
+	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 300UL * HZ);
 
 	if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
 		WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
@@ -428,6 +428,35 @@ static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp
 	return j > 2 * HZ;
 }
 
+static void print_cpu_stat_info(int cpu)
+{
+	struct rcu_snap_record rsr, *rsrp;
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+	struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu);
+
+	if (!rcu_cpu_stall_cputime)
+		return;
+
+	rsrp = &rdp->snap_record;
+	if (rsrp->gp_seq != rdp->gp_seq)
+		return;
+
+	rsr.cputime_irq     = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
+	rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
+	rsr.cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
+
+	pr_err("\t         hardirqs   softirqs   csw/system\n");
+	pr_err("\t number: %8ld %10d %12lld\n",
+		kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs,
+		kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs,
+		nr_context_switches_cpu(cpu) - rsrp->nr_csw);
+	pr_err("\tcputime: %8lld %10lld %12lld   ==> %d(ms)\n",
+		div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC),
+		div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC),
+		div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC),
+		jiffies_to_msecs(jiffies - rsrp->jiffies));
+}
+
 /*
  * Print out diagnostic information for the specified stalled CPU.
  *
@@ -484,6 +513,8 @@ static void print_cpu_stall_info(int cpu)
 	       data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
 	       rcuc_starved ? buf : "",
 	       falsepositive ? " (false positive?)" : "");
+
+	print_cpu_stat_info(cpu);
 }
 
 /* Complain about starvation of grace-period kthread.  */
@@ -588,7 +619,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
+	pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
 	       smp_processor_id(), (long)(jiffies - gps),
 	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 	if (ndetected) {
@@ -649,7 +680,7 @@ static void print_cpu_stall(unsigned long gps)
 	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
+	pr_err("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
 		jiffies - gps,
 		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 

kernel/rcu/update.c

@@ -144,8 +144,45 @@ bool rcu_gp_is_normal(void)
 }
 EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
 
-static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
+static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1);
+/*
+ * Should call_rcu() callbacks be processed with urgency or are
+ * they OK being executed with arbitrary delays?
+ */
+bool rcu_async_should_hurry(void)
+{
+	return !IS_ENABLED(CONFIG_RCU_LAZY) ||
+	       atomic_read(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_should_hurry);
+
+/**
+ * rcu_async_hurry - Make future async RCU callbacks not lazy.
+ *
+ * After a call to this function, future calls to call_rcu()
+ * will be processed in a timely fashion.
+ */
+void rcu_async_hurry(void)
+{
+	if (IS_ENABLED(CONFIG_RCU_LAZY))
+		atomic_inc(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_hurry);
 
+/**
+ * rcu_async_relax - Make future async RCU callbacks lazy.
+ *
+ * After a call to this function, future calls to call_rcu()
+ * will be processed in a lazy fashion.
+ */
+void rcu_async_relax(void)
+{
+	if (IS_ENABLED(CONFIG_RCU_LAZY))
+		atomic_dec(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_relax);
+
+static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
 /*
  * Should normal grace-period primitives be expedited?  Intended for
  * use within RCU.  Note that this function takes the rcu_expedited
@@ -195,6 +232,7 @@ static bool rcu_boot_ended __read_mostly;
 void rcu_end_inkernel_boot(void)
 {
 	rcu_unexpedite_gp();
+	rcu_async_relax();
 	if (rcu_normal_after_boot)
 		WRITE_ONCE(rcu_normal, 1);
 	rcu_boot_ended = true;
@@ -220,6 +258,7 @@ void rcu_test_sync_prims(void)
 {
 	if (!IS_ENABLED(CONFIG_PROVE_RCU))
 		return;
+	pr_info("Running RCU synchronous self tests\n");
 	synchronize_rcu();
 	synchronize_rcu_expedited();
 }
@@ -508,6 +547,10 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 module_param(rcu_cpu_stall_timeout, int, 0644);
 int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
 module_param(rcu_exp_cpu_stall_timeout, int, 0644);
+int rcu_cpu_stall_cputime __read_mostly = IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME);
+module_param(rcu_cpu_stall_cputime, int, 0644);
+bool rcu_exp_stall_task_details __read_mostly;
+module_param(rcu_exp_stall_task_details, bool, 0644);
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 
 // Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
@@ -555,9 +598,12 @@ struct early_boot_kfree_rcu {
 static void early_boot_test_call_rcu(void)
 {
 	static struct rcu_head head;
+	int idx;
 	static struct rcu_head shead;
 	struct early_boot_kfree_rcu *rhp;
 
+	idx = srcu_down_read(&early_srcu);
+	srcu_up_read(&early_srcu, idx);
 	call_rcu(&head, test_callback);
 	early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
 	call_srcu(&early_srcu, &shead, test_callback);
@@ -586,6 +632,7 @@ static int rcu_verify_early_boot_tests(void)
 		early_boot_test_counter++;
 		srcu_barrier(&early_srcu);
 		WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
+		cleanup_srcu_struct(&early_srcu);
 	}
 	if (rcu_self_test_counter != early_boot_test_counter) {
 		WARN_ON(1);

kernel/sched/core.c

@@ -5342,6 +5342,11 @@ bool single_task_running(void)
 }
 EXPORT_SYMBOL(single_task_running);
 
+unsigned long long nr_context_switches_cpu(int cpu)
+{
+	return cpu_rq(cpu)->nr_switches;
+}
+
 unsigned long long nr_context_switches(void)
 {
 	int i;

kernel/torture.c

@@ -450,7 +450,7 @@ unsigned long
 torture_random(struct torture_random_state *trsp)
 {
 	if (--trsp->trs_count < 0) {
-		trsp->trs_state += (unsigned long)local_clock();
+		trsp->trs_state += (unsigned long)local_clock() + raw_smp_processor_id();
 		trsp->trs_count = TORTURE_RANDOM_REFRESH;
 	}
 	trsp->trs_state = trsp->trs_state * TORTURE_RANDOM_MULT +
@@ -915,7 +915,7 @@ void torture_kthread_stopping(char *title)
 	VERBOSE_TOROUT_STRING(buf);
 	while (!kthread_should_stop()) {
 		torture_shutdown_absorb(title);
-		schedule_timeout_uninterruptible(1);
+		schedule_timeout_uninterruptible(HZ / 20);
 	}
 }
 EXPORT_SYMBOL_GPL(torture_kthread_stopping);

tools/testing/selftests/rcutorture/bin/configcheck.sh

@@ -10,10 +10,9 @@
 T="`mktemp -d ${TMPDIR-/tmp}/configcheck.sh.XXXXXX`"
 trap 'rm -rf $T' 0
 
-cat $1 > $T/.config
+sed -e 's/"//g' < $1 > $T/.config
 
-cat $2 | sed -e 's/\(.*\)=n/# \1 is not set/' -e 's/^#CHECK#//' |
-grep -v '^CONFIG_INITRAMFS_SOURCE' |
+sed -e 's/"//g' -e 's/\(.*\)=n/# \1 is not set/' -e 's/^#CHECK#//' < $2 |
 awk	'
 {
 		print "if grep -q \"" $0 "\" < '"$T/.config"'";

tools/testing/selftests/rcutorture/bin/console-badness.sh

@@ -10,7 +10,7 @@
 #
 # Authors: Paul E. McKenney <paulmck@kernel.org>
 
-egrep 'Badness|WARNING:|Warn|BUG|===========|BUG: KCSAN:|Call Trace:|Oops:|detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state|rcu_.*kthread starved for|!!!' |
+grep -E 'Badness|WARNING:|Warn|BUG|===========|BUG: KCSAN:|Call Trace:|Oops:|detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state|rcu_.*kthread starved for|!!!' |
 grep -v 'ODEBUG: ' |
 grep -v 'This means that this is a DEBUG kernel and it is' |
 grep -v 'Warning: unable to open an initial console' |

tools/testing/selftests/rcutorture/bin/kvm-build.sh

@@ -44,10 +44,10 @@ fi
 ncpus="`getconf _NPROCESSORS_ONLN`"
 make -j$((2 * ncpus)) $TORTURE_KMAKE_ARG > $resdir/Make.out 2>&1
 retval=$?
-if test $retval -ne 0 || grep "rcu[^/]*": < $resdir/Make.out | egrep -q "Stop|Error|error:|warning:" || egrep -q "Stop|Error|error:" < $resdir/Make.out
+if test $retval -ne 0 || grep "rcu[^/]*": < $resdir/Make.out | grep -E -q "Stop|Error|error:|warning:" || grep -E -q "Stop|Error|error:" < $resdir/Make.out
 then
 	echo Kernel build error
-	egrep "Stop|Error|error:|warning:" < $resdir/Make.out
+	grep -E "Stop|Error|error:|warning:" < $resdir/Make.out
 	echo Run aborted.
 	exit 3
 fi

tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh

@@ -32,11 +32,11 @@ for i in ${rundir}/*/Make.out
 do
 	scenariodir="`dirname $i`"
 	scenariobasedir="`echo ${scenariodir} | sed -e 's/\.[0-9]*$//'`"
-	if egrep -q "error:|warning:|^ld: .*undefined reference to" < $i
+	if grep -E -q "error:|warning:|^ld: .*undefined reference to" < $i
 	then
-		egrep "error:|warning:|^ld: .*undefined reference to" < $i > $i.diags
+		grep -E "error:|warning:|^ld: .*undefined reference to" < $i > $i.diags
 		files="$files $i.diags $i"
-	elif ! test -f ${scenariobasedir}/vmlinux && ! test -f "${rundir}/re-run"
+	elif ! test -f ${scenariobasedir}/vmlinux && ! test -f ${scenariobasedir}/vmlinux.xz && ! test -f "${rundir}/re-run"
 	then
 		echo No ${scenariobasedir}/vmlinux file > $i.diags
 		files="$files $i.diags $i"

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -186,7 +186,7 @@ do
 		fi
 		;;
 	--kconfig|--kconfigs)
-		checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\)*$' '^error$'
+		checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\|"[^"]*"\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\|"[^"]*"\)\)*$' '^error$'
 		TORTURE_KCONFIG_ARG="`echo "$TORTURE_KCONFIG_ARG $2" | sed -e 's/^ *//' -e 's/ *$//'`"
 		shift
 		;;
@@ -585,7 +585,7 @@ awk < $T/cfgcpu.pack \
 echo kvm-end-run-stats.sh "$resdir/$ds" "$starttime" >> $T/script
 
 # Extract the tests and their batches from the script.
-egrep 'Start batch|Starting build\.' $T/script | grep -v ">>" |
+grep -E 'Start batch|Starting build\.' $T/script | grep -v ">>" |
 	sed -e 's/:.*$//' -e 's/^echo //' -e 's/-ovf//' |
 	awk '
 	/^----Start/ {
@@ -622,7 +622,7 @@ then
 elif test "$dryrun" = sched
 then
 	# Extract the test run schedule from the script.
-	egrep 'Start batch|Starting build\.' $T/script | grep -v ">>" |
+	grep -E 'Start batch|Starting build\.' $T/script | grep -v ">>" |
 		sed -e 's/:.*$//' -e 's/^echo //'
 	nbuilds="`grep 'Starting build\.' $T/script |
 		  grep -v ">>" | sed -e 's/:.*$//' -e 's/^echo //' |

tools/testing/selftests/rcutorture/bin/parse-console.sh

@@ -65,7 +65,7 @@ then
 	fi
 
 	grep --binary-files=text 'torture:.*ver:' $file |
-	egrep --binary-files=text -v '\(null\)|rtc: 000000000* ' |
+	grep -E --binary-files=text -v '\(null\)|rtc: 000000000* ' |
 	sed -e 's/^(initramfs)[^]]*] //' -e 's/^\[[^]]*] //' |
 	sed -e 's/^.*ver: //' |
 	awk '
@@ -128,17 +128,17 @@ then
 	then
 		summary="$summary  Badness: $n_badness"
 	fi
-	n_warn=`grep -v 'Warning: unable to open an initial console' $file | grep -v 'Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process' | egrep -c 'WARNING:|Warn'`
+	n_warn=`grep -v 'Warning: unable to open an initial console' $file | grep -v 'Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process' | grep -E -c 'WARNING:|Warn'`
 	if test "$n_warn" -ne 0
 	then
 		summary="$summary  Warnings: $n_warn"
 	fi
-	n_bugs=`egrep -c '\bBUG|Oops:' $file`
+	n_bugs=`grep -E -c '\bBUG|Oops:' $file`
 	if test "$n_bugs" -ne 0
 	then
 		summary="$summary  Bugs: $n_bugs"
 	fi
-	n_kcsan=`egrep -c 'BUG: KCSAN: ' $file`
+	n_kcsan=`grep -E -c 'BUG: KCSAN: ' $file`
 	if test "$n_kcsan" -ne 0
 	then
 		if test "$n_bugs" = "$n_kcsan"
@@ -158,7 +158,7 @@ then
 	then
 		summary="$summary  lockdep: $n_badness"
 	fi
-	n_stalls=`egrep -c 'detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state' $file`
+	n_stalls=`grep -E -c 'detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state' $file`
 	if test "$n_stalls" -ne 0
 	then
 		summary="$summary  Stalls: $n_stalls"